Field of the Invention
The present invention relates to a new and improved microbial growth inhibition test for the determination of the presence or absence of an antibiotic in a sample such as milk.
Description of Related Art
Nowadays, antibiotics are frequently used in veterinary practice not only for treatment of bacterial infections, but also for prophylactic purposes to improve the productivity of foodstuffs. In recent years, this irresponsible misuse of antibiotics as a preventive measure has been a decisive factor favoring the growth of bacterial resistance.
Antibiotic residues are known to be among the most frequently detected contaminants in milk and dairy products and cause important problems in this industrial sector at economical level.
To prevent the negative impact of antibiotic residues on human health and on the entire ecosystem, microbial growth inhibition tests for the determination of the presence or absence of antibiotic residues in a sample have been developed. Examples of such tests have been described in for example EP 0 005 891A and EP 0 285 792A. The tests described therein are ready-to-use tests that make use of a test organism and an indicator molecule, for instance a pH- and/or redox-indicator. The general principle of the test is that, when an antibiotic is present in a sample in a concentration sufficient to inhibit growth of the test organism, the color of the indicator will stay the same, while, when no inhibition occurs, growth of the test organism is accompanied by the formation of acid or reduced metabolites or other phenomena that will induce an indicator signal.
In general a microbial growth inhibition test will give a result within 2.5 to 4.5 hours. The long test duration is often considered as a disadvantage of microbial growth inhibition tests. Due to the long test duration, the user needs to wait for a long time for the outcome of the test and consequently further delivery or processing of the product to be tested is delayed.
In EP 0 755 456A it has been described that the duration of a microbial growth inhibition test can be reduced by using a concentration of test organism higher than 107 per ml. WO 94/18343 describes that a reduction of the test duration can be achieved when a combination of two or more indicators is used. The disadvantage of both methods is that the sensitivity of the test is decreased. Furthermore, the solutions provided are too expensive.
In view of the above, there is still a need for a microbial growth inhibition test with a reduced test duration.